The Determination of Arsenic in Hydrochloric and Sulfuric Acids

R. F. Tarbell. Ind. Eng. Chem. , 1914, 6 (5), pp 400–401. DOI: 10.1021/ie50065a013. Publication Date: May 1914. ACS Legacy Archive. Cite this:Ind. E...
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lead sulfate precipitate. These elements form, when treated with sodium hydroxide solution, insoluble silver oxide a n d bismuth hydroxide which are readily soluble in dilute nitric acid. T o keep these from going in with t h e lead solution, a n d a t t h e same time t o purify t h e filter paper from t h e lead, it was found necessary, after t h e filtration of t h e solution obtained by t h e t r e a t m e n t of t h e lead sulfate with t h e sodium hydroxide, t o remove t h e filtrate a n d t r e a t t h e residue a n d filter paper with hot water slightly acidifie‘d with nitric acid. The filtrate obtaine’d by this treatment is made quite strongly alkaline with sodium hydroxide a n d filtered through t h e same filter paper. From t h e combined filtrates t h e lead iodate is precipitated. The following experiments show t h a t these elements, when t h e treatment is made according t o t h e above modifications of t h e outline scheme, have no effect upon t h e accuracy of t h e results. Ferric iron is not readily precipitated as t h e iodate in presence of nitric acid also has no effect upon t h e results. G . PbSOa taken 0.3 0.3 0.3

G . AgpS04 G. Fe:(SOi)a G. BiZ(SO1)a G. P b in taken taken PbSOl taken 0.1 ... 0.1 0.2049 0.1






0.2049 0,2049

G. P b found 0.2047 0.2043 0,2051

Vol. 6, No. 5

known volume of a n iodine-in-gasoline solution of known strength. The excess of iodine is reduced b y adding a known amount of a sodium arsenite solution a n d then titrated back with a n iodine solution using starch as indicator. The writer has found t h a t b y this method one atom of arsenic is equivalent t o eight atoms of iodine. This would correspond t o t h e following equations: AsH3 31z = As13 3HI 2ASI3 3 H 2 0 = As203 6HI .%Szo3 212 zH20 = As205 4HI

+ + +






A train is connected as follows: A j o o cc. flask is fitted with a two-hole rubber stopper. Through one hole in t h e stopper is fitted a 12: cc. globe-shaped separatory funnel turned up a t its lower end t o prevent t h e escape of gas. Through t h e other hole is fitted a Kjeldahl connecting bulb. This is in t u r n connected with a Koeninck’s potash bulb. The potash bulb is next connected t o a single bulb such as always comes with a n d precedes a Lleyer’s bulb tube. T o this is connected a Meyer’s bulb tube. There should be a t hand a 5 0 0 cc. Squibb’s pear-shaped separatory funnel. R E A G E N T S AND STANDARD SOLUTIONS

T h e determination of lead in a n ore by this method can be made in 4 j minutes t o one hour’s time. The cost of t h e reagents in t h e determination is not excessive, a n d should not exceed a few cents per determination when 0 . ; t o I gram samples are used. For low-grade lead ores t h e cost is materially reduced because of t h e smaller quantity of potassium iodate required. Some of t h e advantages of, t h e determinations are rapidity of manipulation, definiteness of t h e reactions of titration, non-interference of t h e elements usually associated with lead minerals a n d exactness of t h e end point. SOUTH DAKOTASTATESCHOOLOF M I N E S RAPID CITY


I t is always necessary in the manufacture and purchase of hydrochloric a n d sulfuric acids t h a t are t o be used in t h e preparation of food products to make some sort of test t o determine t h e percentage of arsenic present. T h e writer has worked out a method which he has found very satisfactory a n d accurate. Once the apparatus is set up a n d the standard solutions and reagents prepared, a determination requires very little a t t e n tion. P R I N C I P L E S IN V 0 LT‘E D

It is well known t h a t arsine and iodine react t o gether under certain conditions forming arsenious iodide. This reaction seems t o hold when t h e iodine is dissolved i p specially prepared gasoline. I n t h e following method arsine is generated in the usual way, passed through a solution of lead acetate t o remove a n y hydrogen sulfide formed a n d then passed through a

Gasoline--A quantity of gasoline is prepared from ordinary 60’ gasoline in t h e following way: Fill a gallon bottle three-fourths full of the gasoline a n d a d d zoo cc. c. P. sulfuric acid. Stir this eight or t e n hours with air, let settle, pour off t h e gasoline i n t o a similar bottle, a d d 2 0 0 cc. c . P . sulfuric acid a s before a n d let s t a n d several days with occasional shaking. Pour t h e gasoline from t h e acid, a d d a dilute solution of sodium hydroxide a n d agitate ten or fifteen minutes t o neutralize all acid. Wash gasoline with water, let settle, a n d when clear it is ready for use. Sta?zizous Chloride Solution-Dissolve z j grams c. P . tin in arsenic-free hydrochloric acid a n d evaporate almost t o dryness. Take up with water a n d make up t o 5 0 0 cc. Arsenic-free Hydrochloric Acid-Dilute C . P . hydrochloric acid t o sp. gr. I . i o , a d d a small amount of either copper sulfate or mercuric chloride and precipitate with hydrogen sulfide. Let s t a n d four or five days, filter a n d distil. Alkaline Sodium Arsertite Solutioiz-Dissolve 0.2640 gram pure arsenious oxide a n d I gram sodium carbonate in I O O cc. hot water. After cooling, a d d I gram sodium bicarbonate and make total volume I liter with water. Iodine Solutioit-Dissolve 0 . 6 7 7 3 gram pure iodine and i . 2 grams potassium iodide in water a n d make t h e volume up t o i liter. I o d in e- iIZ - C: .Is ol in e S o l z ~i of iz- Dissolve 0.6 7 7 3 gra m pure iodine in the prepared gasoline and make t h e volume up t o I liter with gasoline. Zinc-Use c. P. arsenic-free stick zinc. METHOD O F ANALYSIS

Fill t h e potash bulb with lead acetate solution t o t h e top of t h e first bulb. P u t 2 0 cc. iodine-in-gasoline



LIaY, 1914

solution, 80 cc. gasoline a n d 2 0 cc. water into t h e bulb tubes. Place a stick of zinc weighing a b o u t 35 grams in t h e flask a n d connect t h e apparatus, seeing t h a t all joints are tight. Weigh o u t a b o u t 25 grams of t h e acid t o be tested. T h e weight of sample a n d t h e q u a n t i t y of iodine-in-gasoline solution used will of course v a r y with t h e arsenic content of t h e acid, b u t a little experience will enable t h e operator t o adjust these quantities. If hydrochloric acid, i t s specific gravity should be m a d e a b o u t 1.10 b y adding either water or arsenic-free hydrochloric acid as m a y be necessary. If sulfuric acid, i t s specific gravity should be m a d e a b o u t 1.40 b y adding either water or c. P . sulfuric acid as m a y be necessary. Pour t h e sample through t h e separatory funnel i n t o t h e flask. T h e n pour I cc. stannous chloride solution through t h e funnel. Pour through enough water t o wash t h e funnel. Close t h e stopcock a n d let t h e reactions proceed with all connections t i g h t for a b o u t z hours, heating t h e flask on a water b a t h if t h e action becomes t o o slow. T h e n a d d 2 0 cc. c. P. sulfuric acid (sp. gr. 1.40) through t h e separatory funnel a n d allow t h e test t o proceed for I hour more. E m p t y t h e cont e n t s of the bulb t u b e into t h e 500 cc. separatory funnel. Wash t h e bulb t u b e with water into t h e same funnel. R u n o u t t h e water from below a n d a d d 20 cc. sodium arsenite solution t o t h e contents of the funnel. Shake till t h e solution is colorless. allow t o settle into t w o layers a n d draw off t h e lower layer into a white dish. Add starch indicator a n d t i t r a t e with t h e iodine solution in t h e regular way: I cc. iodine solution = I cc. sodium arsenite solution = I cc. iodine-in-gasoline solution = o.oooo j g r a m arsenic.

40 1

Decennial Revision), pages 39 j t o 396, point o u t t h e fact t h a t low results are often obtained in t h e assay of peppermint oil. One possible source of error t h a t seems t o have received no attention is t h e low efficiency of t h e reflux condenser t h a t is employed when t h e oil is boiled for one hour with a N,‘2 alcoholic solution of potassium hydroxide, in t h e determination of menthol as ester; a n d later i n t h e method when t h e oil is boiled for one hour with acetic acid anhydride, a n d also when t h e acetylized oil is boiled for one hour with a N,/2 alcoholic solution of potassium hydroxide, i n t h e determination of t o t a l menthol. Any oil lost through incomplete condensation would, obviously, cause low results. Therefore, a number of determinations of menthol as ester a n d of t o t a l menthol were made on six different samples of peppermint oil obtained from as m a n y sources. T h e three forms of condenser illustrated were used. I n Fig. I is shown t h e Allihn condenser.



0.02 0 02 0.05 0.05

0.10 0.10 0.25 0.3i

Mg. I Rlg. As t &en by As found 0..14

0.27 0.61 0.74 1.15 I .42

2.08 4.86

0 .0 2 0.02 0.04

0.05 0.08 0.10 0.21


Mg. As Mg.I taken taken by .is

hlg. As

found 0.50

0.50 0.50 1 .no 1.00

6.i3 6.42 13.45


0 . 9.5

1.88 2.50

2 5 12 34.0;

1.85 2.51


50. 58







A number of analyses were made using different volumes of solutions of sodium arsenite of known strength. Kahlbaum’s arsenious oxide was used in making these solutions. T h e numbers in t h e last column are obtained b y multiplying t h e figures in t h e second column b y 0.07382. NATIOKAL Z I N C COMPANY K A N S A S C:TY, R A M A S


Xrticles in Hygieizic Labovatory Bulletin, N o . 49, “Digest of Comments on t h e Pharmacopoeia of t h e United States of America’’ ( E i g h t h Decennial Revision), pages 2 2 2 a n d 223, a n d i n Hygiertic L a b o r a t o r y Bulletin No. 75, “ Digest of Comments on t h e P h a r m a copoeia of t h e United States of America” (Eighth



I n Fig. 2 is shown t h e Chamot-Soxhlet glass ball condenser. T h e device at F is worthy of mention as i t enables t h e experimenter t o see at a glance how much water is flowing through t h e condenser. I n Fig. 3 is shown t h e Fritz Friedrichs condenser, which m a y be used as a reflux condenser b y allowing t h e vapor t o enter at C , or which m a y be used in di’stillations b y allowing t h e vapor t o enter at D. T h e water for cooling enters through A E a n d escapes through B. EXPERIMEKT I-A peppermint oil was used t h a t h a d a specific gravity of 0.90j6 a t 2 j o a n d showed a polarization of -19.87 a t 2 j ’. E q u a l volumes of t h e oil were weighed in three 1 2 j cc. flasks a n d t h e required amounts of iV/2 alcoholic potassium hydroxide added. I n t o t h e neck of one of t h e flasks was inserted a n Allihn condenser, into t h e neck of another was inserted a Chamot-Soxhlet condenser. a n d into t h e neck of t h e third was inserted a Fritz Friedrichs coildenser. T h e outlet D of each condenser was loosely plugged with cotton wool. T h e condensers were connected in series,